The present invention relates to a vacuum interrupter and more particularly to an improved electrode structure for a vacuum interrupter. Still more particularly, the invention relates to an improved tubular coil conductor forming a part of the electrodes for a vacuum interrupter.
A vacuum interrupter for handling a high current generally includes a pair of main electrodes disposed in a vacuum vessel so that at least one of the pair is movable toward and away from the other, coil conductors mounted on the rear surfaces of the main electrodes, and conductor rods extending to the exterior of the vacuum vessel from the rear surfaces of the coil conductors. Current flows from one of the conductor rods to the other through the coil conductors and main electrodes. When one of the conductor rods is urged by an actuator for the purpose of interrupting the current, at least one of the main electrodes is moved away from the other, and an arc current is caused to flow between the spaced electrodes. This arc current is dispersed into a plurality of filament-like arc currents by a magnetic field created by the flow current through the coil conductors.
U.S. Pat. No. 3,946,179 discloses a coil conductor that comprises a plurality of conductive arms connected to arcuate sections. The arms connect at one end to a conductor rod and diverge in a generally radial direction therefrom to connect to an arcuate section at the other end. The arcuate sections extend circumferentially from the arms and connect to a main electrode. A plurality of arms and associated arcuate sections with clearances formed between adjacent arcuate sections, form an imaginary coil of one turn. Current flows from the rod to the main electrode through the spaced arms and associated arcuate sections. The one-turn current produces a uniform axial magnetic field that produces the diffuse, filamentary arc currents between the main electrodes.
The use of the clearance in U.S. Pat. No. 3,946,179 to produce the coil effect in the coil conductor results in a weak axial magnetic field in the region of the clearances. Arc currents have a tendency to migrate from a low intensity region toward a high intensity region of an axial magnetic field. Thus, the arc current flowing into the main electrode migrates away from the region of the clearances, causing localized overheating of the main electrode. In addition, because the entire area of the main electrode cannot be utilized effectively for the current interruption, it becomes necessary to increase the size of the main electrode.
In commonly assigned U.S. Ser. No. 156,251, a uniform axial magnetic field is produced by providing parallel slits in the coil conductors. However, the configuration of the coil conductors still provide certain limitations in the size of the axial magnetic field that may be generated. The axial magnetic field is partially cancelled by a radial magnetic field, which is generated by current flow through the bottom of the diverging coil conductors. Furthermore, the structure of the coil conductors may be susceptible to mechanical fatigue.